Television synchronizing system



AUI JM W. D. HOUGHTON TELEVISION SYNCHRONIZING SYSTEM Filed March 2'7,1958 MMM. f

July 5, 1960 ffm/ri?! War/winrar INVEN TOR.

WILLIAM D. Hnuaa'rnn generated signal.

United States Patent TELEVISION SYNCHRONIZING 'SYSTEM yWillamD.Houghton, Princeton, NJ., assignor to Radio Corporation of America, acorporation of Delaware Filed Mar. 27, 1958, Ser. No. 724,458

7 Claims. (Cl. v178-'6.\5)

This invention relates to-a system 'for providing-fautomaticsynchronization of television signals derived vfrom'a movable storagemedium.

AMore particularly, the invention deal-s with a synchronizingvarrangement for a television transmission system in vwhich it is desiredto interchangeably transmit either la television signal derived from amagnetic tape or a locally generated television signal in such a manneras to `obviate any 4discontinuity in-the series of signal transltheimage pickup equipment for synchronization of its scanning action in theproduction of the video signal. The synchronizing and blankinginformation is then cornbined with the resulting video signal to producethe composite signal for modulation of the television transmitter.

When it is desired to transmit or retransmit program ,materialpreviously recorded on a magnetic tape, for eX- ample, it becomesdesirable to supply some means for locking or timing the local syncgenerator signals with the signal recovered from the magnetic tape.locked -feature generally is necessary because the signal recorded ontape may have been generated originally on a different frequencystandard from that of the llocally Further, the dilii'culty of drivingthe tapesystem at the particular speed required to maintain synchronismbetween synchronizing signals recovered lfrom the tape and the locallygenerated'synchronizing signals is very great. If no Vtime-lockingfeature were provided, switching between a locally generated programmaterial source and a recovered program material source would likelyresult in a disturbance in the reproduced television image at televisionreceivers due to discontinuity in synchronizing information applied tothe television receiver beam deflection system.

Moreover, in the transmission of special eiects such as lap dissolves,video wipes, or composite pictures .produced by the superimposition ofthe recovered tape signal and the locally generated signal, it isnecessary to maintain precise synchronization and -accurate phasingbetweenthe two signals undergoing the special effects process. Forexample, it is well known that `failure to maintain proper lock-inbetween the two superimposed television signals will create the effectof one picture drifting past the other.

As a solution to such a problem, one possible arrangement is to `use therecovered tape sync signals as the standard. The sync signals for thelocally derived image signals are then tied to or genlocked to therecovered tape This time- Y :magnetic tape, is recovered fromthe tape.

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sync signals, but due to tape dropout (resulting from imperfections inthe magnetized tape coating) and other irregularities which may occur inthe tape signals, the use of s'uch tape derived signals is not presentlydesirable for most purposes.

In the past, sync signals recovered from the tape have been comparedwith a standard sync signal derived from a local source to obtain anerror control voltage to vary the tape capsta-n drive speed. Thus, inreproduction, the video signals from the tape are phase-locked to thehorizontal pulses from a local sync generator by ymeans of a servocontrolled tape drive system. This unit operates to maintain a Xed timerelation between Vthe reproduced tape horizontal sync pulses and thelocal sync genera- 'tor yhorizontal pulses. This is accomplished ybyphase comparing the two pulse trains in a pulse phase 'comparatornetwork. The error signal output from the phase comparator is then usedto control the tape Velocity Vso as to maintain the required registrybetween the horizontal sync signals. When the reproduced horizon- 'talSync signal isthus locked tov thesync vgenerator hori- 'zontal output,the reproduced video signalsare `also phasellocked to the local syncgenerator pulses. Y y

However, with the above arrangement, only thehori- 'zontal lock -is madeautomatically and vertical framing is 'accomplished by manually openingthe servo loopand allowing the `tape speed to change until'verticalregistry is obtained. When vertical registry is obtained, the loop isagain closed and vertical registry is ymaintained as long as thehorizontal sync pulses are uninterrupted. Since the time required toeffect this framing is 'dependent upon the ability vofthe operator,exact vtiming of the repro- `duced program material becomes verydifficult to achieve.

Further, once 'synchronism is lost, the above manual framing procedure,whichis a relatively slow one, m'ust be again repeated.

It is, therefore, an object 'of this invention to provide a simple meansfor time positioning the television "signals vrecovered from a movablestorage medium relative to followed by horizontal framing-thereof withrespect to locally generated signals with provision for recycling thecomplete operation in case of interruption of either set of signals.

Still another object of the present invention is to provide av `systemfor synchronizing television signals recovered from a magnetic recordingmedium with those derived from a locally generated television signal inconjunction with special effects apparatus so as to improve thereproduced relationship between image components represented by the twotelevision signals.

Another object of the present invention is to provide an improvedtelevision control'syst'em for controlling a magnetic tape reproducingsystem in accordance with synchronizing information derived from anunrelated locally generated composite television signal, said televisioncontrol Vsystem being fully automatic in operation to secure preciseinterlace coincidence between lthe local and tape signals so `as toobviate discontinuties in signal transmission when alternately switchingfrom the local television signal to the reproduced television signal.

ln accordance with the invention, a composite' television The verticaland horizontal synchronizing signals are separated from uit therecovered composite television signal. The recovered vertical syncsignals are then compared to the Vertical sync signals derived from alocal standard synchronizing signal generatorr to provide an errorsignal indicative of any mismatch therebetween. As long as this errorsignal is above a predetermined level, the tape velocity is varied untilregistry between the local and recovered vertical'sync signals isobtained. Next, the tape speed is varied by an error signal derived fromthe comparison of the recovered horizontal sync signals with thestandard locally generated horizontal sync signals.

Thus, during reproduction, the horizontal locking unit is madeinoperative until registry is obtained between the standard verticalsync signal and the recovered vertical sync signal. When such registryis obtained, the horizontal speed control information is automaticallyapplied to the tape drive system and horizontal lockin is therebyestablished. This horizontal locking unit maintains horizontal as wellas vertical'framing as long as the signals are uninterrupted.

In one form of the invention, the error signal employed to obtainregistry between thev two trains of vertical sync signals is apredetermined cyclical control signal which varies the tape speed in apredetermined manner until the .phasediiference between the recoveredvertical sync and the standard vertical sync is reduced below apredetermined value at which time horizontal sync locking control ismade operative.

In another forni of the invention, the error signal employed to obtainvertical sync registry may be that obtained by a phasecomparison of thevertical sync signals.

In either form of the invention, once the horizontal syncsignal'registry is lost and the vertical sync signals become mismatchedbeyond a predetermined amount, the automatic vertical framing controlsystem assumes control until registry is again obtained between thestandard vertical sync signaland the recovered vertical sync signal. Thetape speed control is then returned to the horizontal sync signallocking unit.

The novel features of this invention as well as the invention itself,both as to its organization and method of operation, will best beunderstood from the following description, when read in connection withthe accompanying drawings, in which like reference numerals refer tolike parts, in which:

Figure 1 is a partial block and partial perspective diagram of a framingsystem in accordance with the invention;

4 upon the control current applied to the eddy current brake 20 by abrake control amplifier 24.

The tape 10 is illustrated as having a transducer 26 placed in closeproximity thereto so as to convert magnetic variations recorded on thetape into corresponding electrical variations. It is assumed that thetape 10 contains a record of a composite television signal includingsynchronizing signals recorded in one or more tracks thereon. Thetransducer or pickup head 26 converts the magnetically recordedcomposite television signal into correillustrated as recorded as afrequency modulated carrier Figure 2 is a Avertical sync signal phasecomparator and 'relay control circuit which may be employed in thesystem of Figure l; and Figure 3 is a series of graphs illustrating thewaveforms which occur in the circuit of Figure 2.

The invention will be explained with reference to those parts of aconventional tape recording system which involve the tape drivemechanism and the recovery of signals from the tape such as televisionsignals. For the sake of clarity of illustration, the ground symbolshave been omitted from the block diagrams illustrated in the severaliigures. However, these symbols may =be assumed as being presentwherever necessary to complete a circuit path for current iiow.

.Referring to Figure 1, a movable storage medium 10, for example amagnetic tape, is moved in the direction indicated by the arrow betweena supply reel 12 and a take- `up reel 14. The speed by which themagnetic tape 10 is speed of the capstan drive 16, to that desireddepending it is understood by those skilled in the art that the entiretelevision signal or portions of the signal may be directly recorded onone or more tracks on the tape 10. A typical system for directlyrecording a television signal directly on a magnetic tape is described,for example, in U.S. Patent No. 2,734,941 issued February 14, 1956 to I.A. Zenel. A suitable system wherein a television signal `is separatedinto several portions anddirectly recorded on a magnetic tape isdescribed in an article appearing on page AlO'oi:` the RCA Review ofMarch 1954. The derived composite television signal is amplified by aconventional video amplifier 32 and passed to suitable utilizationcircuits which may, for example, include a television transmitter and/ortypical studio monitoring circuits.

The composite television signal derived from the arnpliiier 32 is alsocoupled to a synchronizing signal separator 34 which may be of the typecommonly found in commercially available television receivers. Atreatment of the general subject may be found in Basic TelevisionPrinciples and Servicing by H. Grob (first edition 1949- AMcGraw Hill)beginning on page 362. The sync separator 34 provides separatedhorizontal synchronizing signals and vertical synchronizing signalswhich are the recovered sync signals from the tape 1t). The recoveredand separated vertical sync signals derived from the sync separator 34are compared in a vertical synchronizing signal phase comparator 36 withhighly stable standard synchronizing signals from a synchronizing signalgenerator 38. The sync generator 38 may be a conventional studio syncgenerator such as the TG-ZA studio sync generator, manufactured by RadioCorporation of America Engineering Products'Department, Camden 2, NewJersey which is described in detail by Instruction Bulletin IB-36l55-1.In the alternative, the sync generator 38 may comprise a source 40 of alocal or distant television signal which is passed through a syncseparator 42 from which horizontal and vertical sync signals areavailable.

In response to any phase deviation of the recovered vertical syncsignals relative to the standard sync signals from the sync generator38, the vertical sync signal phase comparator 36 produces an errorvoltage which is applied through a relay control circuit 44 to thewinding of a relay 46 having an armature 48. Suitable circuitry for thevertical phase comparator 36 and the relay control circuit 44 areillustrated in Figure 2 which will later be described. The function ofthe .relay control circuit 44 is to detect when the error signalgenerated by the vertical phase comparator 36 is reduced below apredetermined minimurn value. The armature 48, when operated byenergization of the windingof the relay 46, couples a cycling voltagesignal from a cycling voltage generator 50 to the brake controlamplifier 24. When deactivated, the armature 48 couples a horizontalerror essaies signal from a horizontal phase comparator 52 'to the yingVoltage capable of varying `the Atape speed through the eddy currentbrake 20` in,y a predetermined manner suchthat the recoveredvertical'syncV signals are varied in time position ahead o'r and behindthe standard vertical sync signals obtained from theY standard syncgener- -ator 38. As the tape speed is varied under control of lthecycling voltage generator 50, a condition is reached wherein thevertical sync signals from the tape signal sub- .stantially coincidewith the vertical sync signals from the When this condition is detectedby the sync generator. Y vertical phase comparator 36 andthe relaycontrol circuit 44, the relay 46 is de-energized, and the horizontalerror signal derived from the horizontal phase comparator 52, is appliedto the eddy current brake 20 for speed control of the tape by thehorizontal sync signals.

The horizontal phase comparator 52v compares the vrecovered horizontalsync signals from the tape 10 with the horizontal sync signals derivedfrom the standard sync vgenerator 38. ln response to any phase deviationof the recovered sync signals from `the standard sync signals,.thehorizontal phase comparator 52 produces an error voltage which isapplied through the brake control amplifier 2 4 to the eddy currentbrake 2i), thereby controlling the speedof the tape 10. Phasecomparators, such as .the horizontal phase comparator 52, are well knownto those-skilled in the television, communication, and allied arts. v'The'automatic frequency `control circuits of many receivers employ phasecomparators extensively. Automatic frequency control circuits such asger-dock, synchroguide, .and synchrolocl are described in theaforementioned book by Grob, page 337 etc., and also in the RCA -syncgenerator instruction book. Thus, if the velocity of the 4tape iiivaries such that the horizontal sync signals recovered therefrom varyfrom the horizontal sync signals of the local sync generator 38, theerror voltage works through the eddy current brake. 29 so as to changethe speed of the tape drive motor 1S and thus, the speed ofthe tapeliti, such that coincidence between-the horizontal sync signals ismaintained.

AIt will be appreciated by 'those skilled in the art, that instead ofthe magnetic, or so-called yeddy current brake illustrated, the errorsignals derived from the phase comparator 52 and the cycling voltageVderived from the generator 50 may be applied through a reactance tubecontrolled oscillator to directly vary the speed of the tape drive motor18. One such systemis described, for example, in U.S. Patent No.2,797,263 issued to Ray M. Dolby, entitled oystem and Method forRecording and Reproducing Records, dated lune 25, 1957.

In Figure 2, the details of the vertical sync signal phase comparator 36andrelay control circuit 44 are illustrated. The function of the circuit`of Figure 2 is to detect the absolute magnitude of any phase differencebetween the Vertical sync signals derived from the standard syncgenerator 38 (Fig.l l) and the vertical sync signals recovered from thetap 10 (Fig. l). As long as this phase difference exceeds apredetermined value, the circuit energizes the relay 46 (Fig. l).Othe1wise,the relay 46 (Fig. l) is de energized and thus allows the tapespeed to be controlled by the horizontal error signal derived fromhorizontal phase comparator 52 (Fig. l). However, during the timeinterval when the vertical sync signals are out of phase by'a`predetermined amount, the tape speed is controlled by the'cyclingvoltage generator Si) (Figure l). The cycling voltage genera-torprovides a cycling control signal whichwenables the vertiealfsync pulsesto rapidly achieve phase coincidence. Thus, assuming that lthe verticalsync signals are negative going, the vertical sync signal 4derived fromthe sync generator 38 (Fig. l) is coupled througha phase inverter 60 toan amplifier 62. In like manner, the vertical sync signals recoveredfrom the 'tape are coupled to yan amplifier 64. The anodes of each ofthe amplifiers 62 and 64 is coupled through an inductance coil 66,properly damped by a resistor 68, to a source of B+ potential 70. Thevalue of the inductance 66 is so chosen in conjunction with the value ofthe damping resistor v68, that, when pulse actuated, the circuitprovides a one cycle rings as illustrated by the comparator outputVAwaveforms (b) and (c) of Figure 3. The anodes` of the amplifiers 62and 64 are also coupled through a differentiating circuit 72 anda diode74 to the input ofA a threshhold amplifier 84. The winding of the relay46 is coupled in the anode circuit of ythe ampliiier 84. The .potentialof the cathode circuit of the threshold amplifier 84 is varied 'with avariable bias means 76.

The operation lof this circuit of Figure 2 will now be described ywithreference to Figure 3 wherein the upper' waveforms illustrate thevertical sync signals appearing at the outputs of the amplifiers 62 and64. The middle waveforms` illustrate the comparator output at the commonpoint 78. Thisvoutput represents the combined ef- -fects of ,thecurrents controlledby each amplifier 62, 64 flowingthrough the commoninductor 66 and resistor 63. The' lower waveforms illustrate the inputto the threshold amplifier S4. The waveform (a) is produced when thevertical sync signals from the two sources are of equal polarity and arein time coincidence. 'In this instance, no output of the comrnon'pointA78 is produced since the sync signals cancel each other, except for aslight disturbance 86 which might occur at the beginning and terminationof the sync signals.

The waveform (b) is produced when the sync signal recovered from thetape precedes the standard sync signal. In the waveform (b), thecomparator output at point 78 appears as a series of single cycleoscillations, each being triggered by the leading and trailing edgesrespectively of the vertical sync signals. The positive going portionsof each of these single cycle oscillations are dilerentiated by thedifferentiating circuit 72, rectified by the diode 74, and the resultingdirect current voltage is applied to the input of the thresholdamplifier 84 as illustrated by the lower Waveform of Figure 3. Thepositive going portions of the voltage pulses of waveform (b) charge thecapacitor 80 through the low irnkpedance ofthe diode 74. The capacitorSti maintains this charge for a time interval determined by the Value ofthe resistor 82 to grid bias the threshold amplifier 84 into .aconducting (ie. on) condition. The threshold amplier 84 remains biasedin 4an on condition until the sync signals substantially coincide andoperate to cancel each other such that the comparator output is reduced4to essentially zero as illustrated in the iirst waveform (a). Theparticular point at which the threshold amplitier ceases conduction isdetermined by the adjustment of the cathode bias control resistor 76.The waveform (c) is produced when the locally lgenerated sync signalprecedes `in time the sync signal recovered from the tape.

Note that the circuit of Figure 2 is one of many that may be employedwith the invention and any other suitable comparator may be employed asdesired.

In another form of the invention, the vertical phase comparator 36 mayinclude a field identification unit of the rtype described in U.S.Patent No. 2,570,775, entitled Electrical Timing Comparator Cir-cuit,issued October 9, 1951, to J. R. DeBaun. The DeBaun patent describesapparatus for distinguishing between what has been designated as evenline and odd line fields. Por example, the line synchronizing pulses ina' standard television signal and at a point in the signal correspondingto the bottom of lthe image or picture, there is provided a series vofsix equaliz-ing pulses cach separated by anY interval 'equivalent toone-half a horizontal line period. This configuration is arbitrarilyassumed to represent the first portion of an even line field scansionrepresentation in as much as the last horizontal line synchronizingpulse is separated from the first equalizing pulse by a full horizontalline interval. Conversely, the odd line fields have been designated asthose wherein the last line synchronizing pulse is separated from thefirst equalizing pulse by only a half line interval.

Thus, if two unrelated composite television signals (one from tape andone lfrom 4a local source) are to be interchangeably transmitted withabsolutely no discontinuity occurring during the switching operation,the two signals have to be in interlace coincidence, i.e. synchronizedon a frame, line and field basis. Stated in another manner, even linefield video signals generated locally are not continuouslyinterchangeable, and thus capable of smooth mixing, with odd line fieldvideo signals recovered from tape. Instead, the even line field videosignals derived from the local source must coincide with the taperecorded even line field video signals. The field detecting circuit ofthe DeBaun reference describes a field distinguishing arrangement whichprovides a 30 cycle per second signal representative of the even linefield pulses in a composite television signal. By thus coupling evenline field pulses derived respectively from the standard sync signalsand the recovered sync signals to the vertical phase comparator 36 (Fig.1), precise interlace coincidence between the recovered and locallygenerated television signals may be obtained.

There has thus been described a very simple arrangement forautomatically obtaining synchronization between the verticalsynchronizing signals obtained from a magnetic tape recorded televisionsignal and a locally generated television signal. Once vertical registryis obtained, control of the tape speed is then switched to a line-bylinecomparison between the horizontal sync signals. If the horizontal syncsignals are lost at any time, the arrangement provides an automaticmeans `for returning control to the vertical sync signals until registrybetween the .vertical signals is again obtained. Also, exact interlacecoincidence is achieved between the video signals derived from `the twosources so that switching from one source to the other may be effectedwithout producing any undesired signal transmission discontinuities.

What is claimed is:

1. In a television system having a composite television signal recordedon a movable storage medium, said television signal including a picturerepresentative component, and line and field synchronizing components7the combination of means for recovering said composite television signalfrom said storage medium, means for separating the line and fieldsynchronizing components from the recovered composite television signal,a source of standard line and field synchronizing components for a localtelevision signal, means for comparing the phase of said separated fieldsynchronizing components with the phase of said standard fieldsynchronizing components, and means for varying the movement of saidstorage medium in a lpredetermined manner until the phase of saidrecovered field synchronizing components and the phase of said standardfield synchronizing components substantially coincide. y

2. In a television system having a composite television signal recordedon a movable storage medium, said television signal including a picturerepresentative component, and line and field synchronizing components,the combination of means for recovering said composite television signalfrom said storage medium, means for separating the line and fieldsynchronizing components from the recovered television signal, a localsource of line and field. synchronizing components for a localtelevision signal, means for comparing the phase of said separatedfield-.synchronizing components with the phase of said local lfleldsynchronizing components, and means for to said first control signal.

varying the speed of movement of said storage medium in a predeterminedcyclical manner until the timing relation between said recovered fieldsynchronizing components and said generated field synchronizingcornponents coincide.

3. In -a television system having a composite television signal recordedon a movable storage medium, said composite television signal includinga picture representative component, and line and field synchronizingcomponents, the combination of means for recovering said compositetelevision signal from said storage medium, means for separating theline and field synchronizing components from the recovered televisionsignal and from one another, a source of standard line and fieldsynchronizing components for a local television signal, means forcomparing the phase of said separated field synchronizing componentswith the phase of said standard field synchronizing components, meansfor comparing the phase of said separated line synchronizing componentswith the phase of said standard line synchronizing components, said lastnamed means being adapted to generate a first control signalrepresentative of the magnitude of the phase difference between each ofsaid line synchronizing components, a source of a predetermined cyclicalsecond control signal, and means to vary the speed of movement `of saidstorage mediumin response to said second control signal in the absenceof coincidence between said field synchronizing components and otherwisein response 4. In a television system having a composite televisionsignal recorded on a movable storage medium and a local source ofstandard synchronizing signals, said signals being of the interlacedvariety including alternate even and odd interlaced field scansionrepresentations, the even field scansion sign-al representations beingidentified by a first configuration of related synchronizing signalsembraced by an adjacent field blanking interval While the odd4 fieldscansion representations are identified by a second and differentconfiguration of related synchronizing signals embraced by the nextconsecutive field blanking interval, each of the synchronizing signalconfigurations including a line component and a field component, thecombination of means for recovering said television signal from saidstorage medium, means for separating the line and field synchronizingcomponents from the recovered television signal and from one another,means coupled to said standard source and to said separating means forcomparing the phase of said separated even field synchronizingcomponents with the phase of said standard even field synchronizingcornponents, line phase comparing means coupled to said standard sourceand to said separating means for comparing the phase of said separatedline synchronizing components with the phase of said standard linesynchronizing components, a source of a predetermined cyclical controlsignal, and means for varying the speed of said storage medium inresponse to said control signal in the absence of substantialcoincidence between said even field synchronizing components andotherwise in response to the phase difference between said linesynchronizing components as determined by said line phase comparingmeans. Y

5. In a television system having a television signal recorded on amovable storage medium and a local television signal source, each ofsaid television signals including a picture representative component,and line and field synchronizing components, the combination of meansfor recovering said television signal from said storage medium, meansfor separating the line and field synchronizing components from therecovered television signal and from one another, mea-ns for separatingthe line and field synchronizing components from the local televisionsignal and from one another, a first signal comparator circuit, meansfor simultaneously applying said recovered separated field synchronizingc0111- ponents and said local separated field synchronizing componentsto said iirst comparator circuit, said irst signal comparator circuitbeing adapted to develop a iirst output control signal in accordancewith the timing relation between said separated iield synchroninzingcomponents, a second signal comparator circuit, means for simultaneouslyapplying said recovered separated line synchronizing components and saidlocal separated line synchronizing components to said second comparatorcircuit, said second comparator circuit being adapted to develop asecond output control signal in accordance with the timing relationbetween said separated line synchronizing components, a source of apredetermined speed control signal, means for controlling the speed ofsaid storage medium in accordance with said predetermined speed controlsignal until said rst control signal indicates coincidence between saidseparated iield synchronizing components and then for controlling thespeed of said storage medium in accordance with said second outputcontrol signal.

6. In a television system having a television signal recorded on amovable storage medium and a local television signal source, each ofsaid television signals ncluding la picture representative component,and line and eld synchronizing components, the combination of means forrecovering said televesion signal from said storage medium, means forseparating the line and field synchronizing components from therecovered television signal and from each other, means for separatingthe line and field synchronizing components from the local televisionsignal ,and from each other, a lirst signal phase comparator circuit,means for simultaneously applying said recovered separated eldsynchronizing components and said local separated eld synchronizingcomponents to said irst comparator circuit, said first signal comparatorcircuit being adapted to develop a first output control signal inaccordance with the timing relation between said sepanated lieldsynchronizing components, a second signal phase comparator circuit,means for simultaneously applying said recovered separated linesynchronizing components and said local separated line synchronizingcomponents to said second comparator circuit, said second comparatorcircuit being adapted to develop a second output control signal inaccordance with the Itiming relation between said separated linesynchronizing components, a source of a predetermined speed controlsignal, and means responsive to said first output control signal toselectively control the speed of said storage medium by saidpredetermined speed control signal and by said second control signal.

7. In a television system having a television signal recorded on amovable storage medium and a local television signal source, each ofsaid television signals including a picture representative component,and line and field synchronizing components, the combination of meansfor recovering said television signal from said storage medium, meansfor separating the line and iield synchronizing components from therecovered television signal and from each other, means for separatingthe line and lield synchronizing components from the local televisionsignal and from each other, a iirst signal cornparator circuit, meansfor simultaneously applying said recovered separated field synchronizingcomponents and said local separated field synchronizing components tosaid first comparator circuit, said first signal comparator circuitbeing adapted to develop a iirst output control signal in accordancewith the timing relation between said separated eld synchronizingcomponents, a second signal comparator circuit, means for simultaneouslyapplying said recovered separated line synchronizing components and saidlocal separated line synchronizing components to said second comparatorcircuit, said second comparator circuit being adapted to develop asecond output control signal in accordance with the timing relationbetween said separated line synchronizing components, a source of acyclical control signal for successively increasing and decreasing thespeed of movement of said storage medium, means for controlling thespeed of said storage medium in accordance with said cyclical controlsignal until said iirst control signal indicates coincidence betweensaid separated ytield synchronizing pulses and then for controlling thespeed of said stortage medium in accordance with said second outputcontrol signal whereby a predetermined timing relation between saidrecovered and said local television signals is maintained automatically.

References Cited in the file of this patent UNITED STATES PATENTS2,727,097 Frayne Dec. 13, 1955 2,774,927 Evans Dec. 18, 1956 2,854,526Morgan Sept. 30, 1958

